Electrodialysing apparatus with supported membranes



Aug. 30, 1960 s. M. PARTRIDGE ELECTRODIALYSING APPARATUS WITH SUPPOTED MEMBRANES Filed March 4, 1957 5 Sheets-Sheet 1 Inventor` im l 5%,mlk FM Attorneys Aug. 30, 1960 S. M. PARTRIDGE ELECTRODIALYSING APPARATUS WITH SUPPORTED MEMBRANES Filed March 4. 1957 5 Sheets-Sheet 2 M, im 9M ,xb

v Attorneys Aug. 30, 1960 s. M. PARTRIDGE ELECTRODIALYSING APPARATUS WITH SUPPORTED MEMBRANES Filed March 4, 1957 5 Sheets-Sheet 3 f P l lnven Jcor` dam Pmi? MAM ,bwfkMMm-Wwkw Attorney s Aug. 30, 1960 s. M. PARTRIDGE ELECTRODIALYSING APPARATUS WITH SUPPORTED MEMBRNES- Filed March 4, 1957 5 Sheets-Sheet 4 Invencor` www Pmly.

Attorneys Aug- 30, 1.960 s. M. PAM-RIDGE '2,951,027

BLECTRODIALYSING APPARATUS WITH SUPPRTED MEMBRANES Filed March 4, 1957'v 5 sheets-sheet 5 FIG-.7.

WWW?? 2 States f nite ELECTRODIALYSING APPARATUS WITH SUPPORTED MEMBRANES Stanley Miles Partridge, Cambridge, England, assignor` to National Research Development Corporation, London, England, a `corporation of Great Britain Filed Mar. 4, 1957, ser. Nb. 643,859-

Claims priority, application vGreat Britain Mar. 6, 19:56

' 2 claims. (c1. zot-302) of channels each of which connects in series a number of perforations in the plates thereby to provide a plurality of compartments in each of said plates; means for supplying a rinsing liquid to the channels and perforations in alternate plates; and means for supplying liquid to be dialysed to the channels and perforations in the remainder of the plates.

The separator plates, which can be made of polythene or other self-gasketing material, not only space the membranes from one another and support the relatively delicate membranes used in a very eicient manner, but also define the working cell Aspace of the apparatus. The channels connecting the compartments formed by the series of perforations in any one plate allow rinsing liquid or liquid to be dialysed to be passed through each of the series of compartments in turn: the liquid thus passes `through a passage having alternate constrictions and enlargements, a design which ensures that adequate mixing takes place in allsections of the passage.

In the accompanying drawings:

Figure 1 is a View, partly in section, illustrating the assembly of an electrodialysing cell constructed according to the present invention,

Figures 2 and 3 are flow diagrams illustrating the circulation of liquid through the cell,

Figure 4 is :an elevation illustrating separator plates forming part of the cell,

Figure 5 is a scrap View to an enlarged scale showing an arrangement of grooves on a separator plate, while Figures 6 and 7 are elevations illustrating plates forming part of electrode compartments in the cell.

The eleotrodialysing cell illustrating in the drawings comprises anode and cathode compartments 1 and 2 respectively between which is an assemblage including a plurality of alternate cation-exchange and anion-exchange non-rigid membranes 3 and 4 respectively spaced `at a short distance from the electrodes by plates 5 of the electrode compartments and spaced a short distance from each other by rectangular separator plates 6 of polythene or other inert resilient material.

Each separator plate 6 has-two slots 7 and 8 running near and parallel to two opposite sides or" the plates, and also has a circular hole 9 in each corner. A plurality of straight grooves l@ in the plates connect the slots to each other: each groove 10 forms a channel which connects in series la number of circular perforations 11 arranged in parallel rows and penetrating the plate, the perforaatentl O 522,951,027: Patented Aug. 30, 1960 tions in one row being staggered relatively to those in the adjacent rows. The perforations 1v1 in each row can be connected by a single groove 10 as shown in Figures 1 and 4 for clarity of illustration. However, -it is preferred that each row of perforations be connected by two grooves on one face of the plate and a single groove on the other face as shown in Figure 5.

The four holes 9 of adjacent separator plates 6 co- Operate to dene four circular manifolds running lengthwise of the cell Aand the slots 7 and 8 of adjacent plates co-operate to define two distributor channels running lengthwise of the cell and connected by the grooves 10 to the plurality of cylindrical compartments formed by the perforations 11 and the alternate anion and cation exchange membranes 3 and 4. The perforations 11 in some of the plates 6 form dialysis compartments and those in the remainder of the plates form rinsing compartments; for convenience, the plates will therefore be hereinafter referred to as dialysis and rinsing plates and denoted 6x and 6y respectively depending on whether during the electrodialysis operations the compartments dened by the plate are dialysis or rinsing compartments.

Conduit grooves 12 in each dialysis plate 6x, connect the slot 7 to one of the adjacent corner holes 9 and the slot 8 is connected by similar grooves 13 to the corner hole 9 diagonally opposite to the first-mentioned corner hole; conduit grooves -14 rand 15 in each rinsing plate 6y connect each slot 7 or 8 to the adjacent corner hole 9 on j the other diagonal. Thus, when the cell is assembled the liquid to be dialysed can be fed through a supply line 16 into the inlet manifold formed by the holes 9 in one corner of all the plates 6, can fiow in each dialysis plate 6x through the grooves 12 into one slot-like distributor channel 7 and via the grooves 10 and perforations 11 (in which de-ioniz'ation occurs) into the other distributor channel 8 and from there through grooves 13 into the manifold formed by the holes 9 at the other end of the diagonal, whence it can be removed through an outlet line 17. Rinsing liquid flows in a similar manner through the rinsing plates 6y, entering the cell through a supply line 18 and leaving it through an outlet line 19. The channels with alternate constrictions and enlargements formed by the grooves 10 and perforations 11 lead to good mixing and a turbulent ow of liquid over the membranes 3 and 4.

The two'electrode compartments 1 and 2 each comprise an end plate 20, a plate-like electrode 21 which may be of platinum foil, the plate 5 and another plate 22. The plates 5 and 22 both have slots 7 and 8, grooves 10 and perforations 11 similar to those in the plates 6 and are separated by a diaphragm 23 which may be a membrane made of ion-exchange material or of regenerated cellulose or other simil-arly permeable material. The free side ofthe plate 5 at the cathode end of the cell is borunded by a cation-exchange membrane and the free side of the plate 5 at the anode end is bound by an anion-exchange membrane 4. The plates 5 and 22 each have two tubular external nipples Z4 communicating with the slots 7 or 8 while the plates 22 have no corner holes 9 and the plates 5 have four more external nipples 25 each of which communicates with one of the four corner holes 9 in that plate.

The design yof the four manifolds formed by the holes 9 and the conduit grooves 12, 13, 14 and 15 is such as to avoid undue loss of electric power due to short-circuitig through the manifolds.

During an electrodialysis operation, an electrode solution of sodium sulphate or other salt which does not give rise to chlorine at the anode is passed (as indicated by arrows ES in Figure 2) through one of the nipples 24 of each plate 5 and thence via the adjacent slot 7 Atrolling the two supplies.

and the grooves and perforations 11 to the other slot 8 whence is passed out of the plate l5 through the other nipple 24 and is led in a similar way past the electrode 21 by owing from the plate 5 through the plate 22. This method of ow prevents acid or alkali produced atthe electrodes 21 from invading the dialysis and rinsing compartments and producing variations in pH. Y

The solution leaving each of thelplates 22 is mixed in order to neutralize the acid and alkali produced, and is scrubbed with a current of air or nitrogen to remove dissolved oxygen or traces of chlorine, and recirculated to the far plates by means of a pump. This scrubbing treatment prevents damage to the membranes by chlorine or high concentrations of oxygen.

The liquid to be de-ionized (denoted by letter S in Figures 2 and 3) is passed under a hydrostatic head of pressure of 3 to 6 feet (controlled by the height of a levelling tube 24) through a metering pump (not shown) in supply line 16 and enters one of the manifolds formed by the holes 9 through one of the nipples 2S of each of the plates 5. It passes upwards through the plates in parallel streams, the lde-ionized liquid leaving the cell through the other nipple 25 on each plate 5 and being recirculated by means of a pump 27 at a rate of recirculation of about 10 to 20 times the rate at which the crude liquid is supplied to the circuit; de-ionized liquid is expelled from the circuit at the same rate at which the crude liquid is supplied, and the electrical current is adjusted to accord with the rate of crude liquid supply and the required degree of deionization. After the ilow has been continued for some time, and an equilibrium state has been reached, the ionic concentration in the circulating liquid is substantially the same as that in the de-ionized liquid leaving the circuit.

There is a corresponding wash water circuit (denoted WW in Figures 2 and 3) for passing wash water through the rinsing compartments, fresh water being supplied through line 18 by means of a metering pump (not shown) and an equal amount of salt-containing Water being expelled through line 19. The expelled water is re-circulated by a pump 2S. The rate of re-circulation is 10 to 20 times the rate at which fresh Water is supplied and after the apparatus has been Working for some time the ionic constitution of the circulating water is substantially the same as that of the spent water discharged. The ratio of the rate iof supply of fresh water to the rate of supply of crude liquid is important and is controlled by adjusting the output of the two metering pumps con- The rate of supply of the crude liquid may be as much as ten times the rate of supply of the fresh water, in which case the ionic concentration of the spent water will be correspondingly increased with respect to that of the crude liquid.

The direction of the flow of the electric current is arranged so that cations leaving the dialysis plates 6x car-rying the liquid pass through a cation-exchanging membrane 3 and anions leaving the dialysis plates pass through an anion-exchanging membrane 4. The cations which migrate into the rinsing plates 6y cannot leave them since they are stopped by the perm-selective properties of the anion-exchanging membrane 4 on its opposite side. The anions which migrate into the rinsing plates are similarly retained therein by the presence of a cationexchanging membrane on its opposite side.

A rate of recirculation of at least 10 times the rate at which crude liquid or fresh water is supplied to the systern ensur uniformity of ilow throughout the plates; it

is also suiiicient to secure a thin diffusion layer at the surface of the membranes but not so large as to require undue expenditure of electric power for operating the pumps. The system of re-circulation used ensures that the solutions in all parts of the separator plates containing the liquid is at substantially the same ionic concentration; similarly the solution in all parts of the separator plates containing wash-Water is at the same ionic concentration.

The arrangement of perforations 11 and grooves 10 in the separator plates 6 ensures adequate support for the membranes 3 and 4 thus increasing the life of the membranes. This is important since va large proportion of the cost of de-ionization by electrodialysis is due to the necessity of replacing the membranes from time to time. 1n addition, the design of the separator plates 6 makes assembly and disassembly of the cell an easy and convenient operation.

The design of the separator plates 6 is such as to allow the passage of slurries containing nely divided material such as are met with in industries handling fluids of biological origin. A feature of the design is that the fluid circulation system is free from slow-flowing pockets which allow such slurries to sediment and thus cause local obstructions of the ow.

What I claim is:

1. In an electrodialyzing apparatus comprising an anode compartment, -a cathode compartment, and an assemblage arranged between the anode compartment and the cathode compartment including a plurality of alternate cation-exchange and anion-exchange non-rigid membranes with a plurality of flat separator plates of inert resilient material arranged between and in contact with adjacent membranes, the improvement wherein each said separator plate has a plurality of perforations providing openings across the thickness of each said plate and a plurality of grooves in the surface of each said plate connecting the perforations of each said plate in spaced vertical series.

2. In an electrodialyzing apparatus comprising an anode compartment, a cathode compartment, and an assemblage arranged between the anode compartment and the cathode compartment including a plurality of alternate cation-exchange and anion-exchange non-rigid membranes with a plurality of at separator plates of inert resilient material arranged between and in contact with adjacent membranes, each of said anode and cathode compartments including a plate-like electrode spaced from the membranes at each end of said assemblage by a at plate of inert resilient material, the improvement wherein each separator plate of said assemblage and each at plate of each compartment includes a plurality of perforations providing openings across the thickness of each said plate and a plurality of grooves in the surface of each said plate connecting the perforations in spaced vertical series.

References Cited in the le of this patent UNITED STATES PATENTS 2,225,024 Weber Dec. 17, 1940 2,735,812 Van Hoek Feb. 21, 1956 2,741,591 Dewey et al Apr. l0, 1956 2,758,083 Van Hoek Aug. 7, 1956 2,784,158 Bodamer et al. .Mar. 5, 1957 FOREIGN PATENTS 682,703 Great Britain Nov. 12, 1952 126,921 Great Britain May 22, 1919 583,474 Germany Sept. 7, 1933 

1. IN AN ELECTRODIALYZING APPARATUS COMPRISING AN ANODE COMPARTMENT, A CATHODE COMPARTMENT, AND AN ASSEMBLAGE ARRANGED BETWEEN THE ANODE COMPARTMENT AND THE CATHODE COMPARTMENT INCLUDING A PLURALITY OF ALTERNATE CATION-EXCHANGE AND ANION-EXCHANGE NON-RIGID MEMBRANES WITH A PLURALITY OF FLAT SEPARATOR PLATES OF INERT RESILIENT MATERIAL ARRANGED BETWEEN AND IN CONTACT WITH ADJACENT MEMBRANES, THE IMPROVEMENT WHEREIN EACH SAID SEPARATOR PLATE HAS A PLURALITY OF PERFORATIONS PROVIDING OPENINGS ACROSS THE THICKNESS OF EACH SAID PLATE AND A PLURALITY OF GROOVES IN THE SURFACE OF EACH SAID PLATE CONNECTING THE PERFORATIONS OF EACH SAID PLATE IN SPACED VERTICAL SERIES. 